At present, the focus of research and development in China is on inorganic flame retardants, microencapsulation of red phosphorus, and expansion flame retardants.
Composite materials based on resin and rubber contain a large amount of organic compounds and have a certain degree of flammability. Flame retardants are a type of additive that can prevent polymer materials from igniting or suppress flame propagation. The most commonly used and important flame retardants are compounds of phosphorus, bromine, chlorine, antimony, and aluminum. Flame retardants can be divided into two categories based on their usage: additive and reactive. Additive flame retardants mainly include phosphate esters, halogenated hydrocarbons, and antimony oxide, which are added to composite materials during processing. They are convenient to use and have a large adaptability, but they have an impact on the performance of composite materials. Reactive flame retardants are added as monomer raw materials to polymer systems during the preparation process, allowing them to be chemically compounded onto polymer molecular chains. Therefore, they have little impact on the properties of composite materials and have long-lasting flame retardancy. Reactive flame retardants mainly include phosphorus containing polyols and halogenated anhydrides.
Flame retardants used for composite materials should have the following properties:
① High flame retardant efficiency, which can endow composite materials with good self extinguishing or flame retardant properties;
② Has good compatibility with composite materials and is easy to disperse;
③ Having a suitable decomposition temperature, that is, it does not decompose at the processing temperature of composite materials, but can rapidly decompose when the composite materials are heated to exert flame retardant effects;
④ Non toxic or low toxic, odorless, non polluting, and does not produce toxic gases during the flame retardant process;
⑤ When used in combination with composite materials, it does not reduce the mechanical properties, electrical properties, weather resistance, and thermal deformation temperature of the composite materials;
⑥ Good durability, able to be retained in composite products for a long time, exerting its flame retardant effect;
⑦ Widely sourced and low-priced.
(1) Bromine based flame retardants include brominated compounds of aliphatic, cycloaliphatic, aromatic, and aromatic aliphatic groups. These flame retardants have high flame retardant efficiency, with a flame retardant effect twice that of chlorine flame retardants. They are used in relatively small amounts and have almost no effect on the mechanical properties of composite materials. They can significantly reduce the content of hydrogen halides in gas. Moreover, these flame retardants have good compatibility with the matrix resin, and even under harsh conditions, there is no spraying phenomenon.
(2) Chlorine based flame retardants are still widely used flame retardants due to their low cost. Chlorinated paraffin with the highest chlorine content is an important flame retardant in industry. Due to its poor thermal stability, it is only suitable for composite materials with processing temperatures below 200 ℃. Chlorinated cyclic hydrocarbons and tetrachlorophthalic anhydride have high thermal stability and are commonly used as flame retardants for unsaturated resins.
(3) Phosphorus based flame retardants and organic phosphides are additive flame retardants. The phosphoric acid generated during the combustion of these flame retardants can form stable oligomers, which cover the surface of composite materials to isolate oxygen and combustibles, and play a flame retardant role. Their flame retardant effect is better than that of bromides. To achieve the same flame retardant effect, the amount of bromide used is 4-7 times that of phosphides. This type of flame retardant mainly includes phosphate esters, halogenated phosphate esters, and halogenated phosphorus salts, which are widely used in epoxy resins, phenolic resins, polyesters, polycarbonates, polyurethanes, polyvinyl chloride, polyethylene, polypropylene, ABS, etc.
(4) Inorganic flame retardants are a type of flame retardant classified according to their chemical structure habits, including antimony oxide, aluminum hydroxide, magnesium hydroxide, and zinc borate.
